The present disclosure relates to systems and methods for digital modulation and demodulation of data in a fiber optic communications system.
Fiber optic channels in network communications systems are well known and are considered effective for data transmission, allowing relatively high bandwidth data communication. Optical fiber used in such channels is flexible and can be bundled as cables, and is generally considered to be appropriate for long-distance communications because light propagates through the fiber with little attenuation compared to electrical cables. Typical present day commercial optical fiber systems transmit data at rates of 10 or 40 Gigabit-per-second. Each fiber can carry multiple independent channels and each of the channels uses a different wavelength of light. This technique, which is known as wavelength-division multiplexing or WDM, enhances the net data rate of an optical fiber. For some dense WDM systems, for example, there may be as many as 80 independent channels with each channel having a 50 Gigahertz channel spacing.
As more capacity is continually desired for networks, a demand for increased data transmission rates exists. As data rates increase in fiber optic systems, however, various optical phenomena begin to manifest and act to limit data transmission rates. Moreover, non-linearities and phase noise issues can affect the performance of certain modulation schemes at the higher data transmission rates.